Previous spring loaded devices, as shown in FIG. 1, include self-centering mechanisms 100 for push-pull control cables 101, which are especially useful for centering controls on hydrostatic and non-detented hydraulic valves used in vehicles.
The spring loaded device of FIG. 1 is a push-pull coaxial cable control mechanism 100, and in particular, a self-centering apparatus that is mounted directly on standard control cables 101 or as part of a new control cable for imparting spring return force to cable members 101 in response to relative movement thereof, out of a predetermined intermediate or neutral position. The conventional spring loaded devices were designed to eliminate bulky dual-spring systems and extra brackets and levers.
In particular, a conventional self-centering spring mechanism is described in detail in U.S. Pat. No. 4,223,564 to Fawcett, the entire contents of which are herein incorporated by reference.
In Fawcett, the self-centering spring mechanism 200 is applied to a push-pull coaxial cable mounted on the end assembly of a control cable 201. The cable 201 terminates in a mounting fixture 202 threaded over a portion of its length to receive jamb nuts 203, 204 designed to clamp against opposite sides of a support such as a mounting panel 205 through which the fixture 202 passes.
The self-centering device 200 includes outer and inner elongated tubular members 206, 207 forming an annular space between them in which an elongated helical spring 208 is received. The spring 208 is partially compressed in the neutral or centered position of the parts.
Actuator rod 209 is threaded over a portion of its projecting length to engage in the threaded socket of a connecting clevis 210 linked by pivot pin 211 to the transmission actuator arm. A jamb nut 212 on the rod 209 bears against the end of the clevis 210 to tighten the connection.
In this conventional cable assembly and its conventional connection by way of the clevis 210 to the transmission shifter arm (not shown) of a hydrostatic drive transmission, relative longitudinal movement of the cable members are effected at a remote point (see 103, FIG. 1), such as in the truck cab, and causes the shifter arm to be moved between its neutral setting (N) and either of the forward (F) and reverse (R) gear positions (see FIG. 2). The stationary mounting panel 205 to which the mounting fixture 202 is secured, takes the reaction force attending forced movement of the shifter arm.
Thus, the self-centering spring device 200 imposes a substantial return force on the shifter arm in response to appreciable displacement of the arm out of position (N), and the force increases as a function of the displacement regardless of the direction in which it occurs.
However, in conventional systems, the spring device 200 is too large in diameter to fit well to the frame of a hydraulic system. Further, the larger end 102 of the spring loaded device 100 (see FIG. 1) has a swivel integrated into it. The cable 101 passes through this swivel into the spring loaded device 100. However, when the spring loaded device 100 is mounted with the smaller end attached to the pedal shaft 103, and the spring cycled, the swivel allows the spring loaded device 100 to collapse when the system causes the inner spring 208 to compress. In other words, the system would work if the spring 208 was extended, but not when the spring 208 was compressed.
Accordingly, a self-centering spring mechanism which would overcome these disadvantages and which would provide a stable and reliable system for centering controls on hydrostatic transmissions and non-detented hydraulic valves, is desired.